This invention relates in general to a novel lubricant used in connection with medical devices such as intravenous (IV) catheters.
IV catheters are designed to infuse normal IV solutions, including antibiotics and other drugs, into a patient. The typical catheter is hollow and is extruded out of a suitable plastic material such as Teflon, polyvinyl chloride, polyethylene, polyurethane or polyether urethane. These catheters are also used to withdraw blood from the patient for normal blood-gas analysis as well as other blood work. In order to insert an IV catheter into a patient, an introducer needle is used. The needle is typically stainless steel and is hollow. Its distal tip is ground to a sharp tip for easy insertion into the patient. The catheter is also hollow and is initially located coaxially around the introducer needle in an "over the needle" arrangement. The internal diameter of the catheter tip is slightly less than the outer diameter of the tip of the needle so that the catheter tip has an interference fit on the needle tip. The interference fit is necessary so that when the catheter and introducer needle assembly is taken out of the package, the catheter remains snugly on the needle and does not easily slip off. This interference fit also facilitates insertion of the catheter and introducer needle assembly into the patient's vein because it minimizes the chance that the catheter tip will fold over or peel back on the needle tip.
Placement of the catheter and introducer needle into the patient may cause sharp pain to the patient. In order to facilitate insertion of the catheter and introducer needle into the vein and to minimize patient discomfort, the catheter and introducer needle can both be lubricated. Most IV catheters are lubricated with polydimethylsiloxane silicone fluid. However, some IV catheters are not lubricated at all.
The polydimethylsiloxane silicone fluid may be applied to the surface of the catheter and needle by wiping the surfaces with the lubricant. Alternatively, the catheter and needle can be separately dipped into a solution of polydimethylsiloxane silicone fluid and a solvent. This is generally the preferred method of applying the lubricant because a consistent, controlled and uniform coating can be achieved. The polydimethylsiloxane silicone fluid must be dissolved in an organic solvent because the silicone oil in this compound is hydrophobic. Typically, the solution contains 2.5% silicone oil. The catheter and needle are then separately dipped into this solution.
Until recently the preferred solvent has been freon because it is non-flammable and flashes off, i.e. evaporates, readily after the polydimethylsiloxane silicone fluid solution has been applied to the catheter and needle. Although freon has been preferred, it does suffer some drawbacks. For instance, the high evaporation rate of freon causes the polydimethylsiloxane silicone fluid to concentrate on the surface of the solution in which the catheter and needle are dipped. Because of this high evaporation rate, the solution is difficult to control. Moreover this solution is expensive because of the large loss of freon during the coating process. In addition, freon is a chlorofluorocarbon (CFC) which is thought to react with and destroy the earth's protective ozone layer. Thus the manufacture and use of such CFC's will eventually cease in the near future.
Other solvents will have to be used in order for silicone fluid to be applied to catheters and introducer needles as a lubricant. Other solvents include alcohol and hydrocarbons. However, alcohol and hydrocarbons are highly combustible and are therefore too dangerous for use in manufacturing.
Previous efforts have been made to provide a lubrication system that uses water as the solvent. Such systems typically are a three part system that uses a lubricant, a surfactant and water. U.S. Pat. No. 5,266,359 discloses such a three part system that uses water as the solvent. Although, such three part lubrication systems that use water as the solvent are "environmentally friendly" and are not flammable, they could be improved. Since a three part lubrication system by definition requires three separate elements, a certain amount of cost is associated with the materials and manufacturing processing needed to apply the system to a medical device to be lubricated.
Another important issue concerning IV catheters is the shape of the catheter tip. The shape of the catheter tip must produce minimal trauma to the patient during insertion of the catheter into the patient and while the catheter is in place in the patient. Such a preferred tip shape that provides these characteristics has a tapered outer wall and an angled tip and is disclosed in U.S. Pat. No. 4,588,398. A process for making that catheter tip is disclosed in U.S. Pat. No. 4,661,300. In this process, the catheter is placed on a mandrel. A die having an interior molding surface, which is tapered according to the tip desired on the catheter, is aligned axially with the mandrel. The catheter tip is heated, typically using RF energy, so that it is flowable. The mandrel and die are brought together so the distal edge of the mandrel engages the tapered portion of the die. This action cleanly forms a smooth and uniform tapered tip for the catheter.
After the catheter is tipped, it must be free of defects such as incomplete formation, substantial flash or jagged edges. The tip must also look smooth and be free of roll-overs. In addition, the length of the catheter must remain within a desired specification after the tipping process. If, during the tipping process, the thermoplastic material sticks to the die or the mandrel, the length will vary greatly due to stretching and the tip will not be free of defects. Visual or microscopic examination may be used to determine if there are any tip defects and if the length of the catheter is within specifications.
Typically a lubricant is used to allow the tipped catheter to be easily removed from the mandrel and die. If a lubricant is not used, the tipped catheter could stick to the mandrel or die resulting in a deformed catheter when it is removed from the mandrel or die. Standard tipping lubricants include polydimethyl siloxanes such as Dow Corning DC 360 or curable silicones such as Dow Corning 44159 MDX which are amine terminated and moisture curable. Non-curable amine terminated polydimethyl siloxanes have also been used for this purpose. Such lubricants are described in, for example, U.S. Pat. Nos. 3,574,673; 4,904,433; and 5,185,006. Again, these silicone oils used are problematic as discussed above.